A buckle has been used as a means for connecting and separating both ends of a fastening string member (e.g. a single belt, tape or thread) or two string members with each other (see, for instance, Patent Literature 1).
Typical buckles include a plug and a socket into which the plug is inserted for engagement. The plug includes a plug body and a pair of legs provided in parallel with each other on both sides of the plug body. A manipulation portion and an engagement portion are provided on an end of each of the legs. The socket includes a socket body and an insertion hole provided in the socket body into which the plug is inserted. Abutment portions to be in contact with each of the legs to cause an inward elastic deformation of each of the legs are provided in the insertion hole. In addition, the insertion hole is provided with engaged portions with which the engagement portions of the legs are engaged and apertures for exposing the manipulation portions of the legs.
In this arrangement, in order for the plug to be engaged with the socket, the legs of the plug are inserted into the insertion hole of the socket. Then, the ends of the legs are inserted while being inwardly elastically deformed by the abutment portions of the socket. When the engagement portions of the legs go beyond the engaged portions provided to the socket, since the inwardly elastically deformed legs are elastically restored outward, the engagement portions of the legs are engaged with the engaged portions provided to the socket. In this state, the manipulation portions of the plug are exposed to an outer surface through the apertures of the socket.
In order to detach the plug from the socket, the manipulation portions of the plug exposed through the apertures of the socket are pressed mutually inward to inwardly elastically deform the legs. Then, the engagement portions of the legs are disengaged from the engaged portions provided to the socket. In this state, the plug is pulled out from the socket. Thus, the plug can be detached from the socket.
Incidentally, since the legs of the plug are deformable inwardly and outwardly in the above buckle, when, for instance, the leg(s) is excessively deformed outward by being caught in an external object, the leg(s) may be outwardly plastically deformed or may be eventually damaged if the leg(s) is forcibly further deformed toward an outside.
In order to remedy the above deficiencies, buckles disclosed in Patent Literatures 2 and 3 include a mechanism for restricting the pair of legs of the plug from deforming to be enlarged outward.
Specifically, Patent Literature 2 discloses a mechanism including a central member provided between a pair of legs (arm members) of the plug in parallel to the legs and curved holder straps (bent portions) connecting the central member and each of the arm members. Patent Literature 3 discloses a mechanism in which the pair of legs of the plug is connected by a curved holder strap (connection belt). According to the mechanisms disclosed in Patent Literatures 2 and 3, when the legs are enlarged outward, since the holder strap(s) is stretched to restrict the arm members from further outward expansion, the damage on the leg(s) can be avoided.